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Horticulture Principles and Practices

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Scale<br />

Compressed<br />

stem<br />

(a) Whole bulb<br />

(b) Cross section<br />

(c) Whole scaly bulb<br />

FIGURE 3–10 A scaly bulb. (Source: George Acquaah)<br />

FIGURE 3–11 Tubers. These<br />

swollen stems vary in size <strong>and</strong><br />

shape depending on the species.<br />

The flesh color is also variable<br />

<strong>and</strong> may be creamish, whitish,<br />

yellowish, or some other color.<br />

(Source: George Acquaah)<br />

(c) Whole tuber of potato<br />

(a) Tuber of Solanum<br />

tuberosum<br />

(b) Tuber of Dioscorea spp.<br />

7. Pseudobulbs. Also called false bulbs, these modified stems are commonly produced<br />

by orchids <strong>and</strong> are variable in appearance. The Dendrobium orchid produces an<br />

elongated <strong>and</strong> jointed structure with offshoots at the upper nodes. Once roots form<br />

at the base of these offshoots, they may be removed <strong>and</strong> transplanted. The most<br />

popular orchids (e.g., Cattleya, Miltonia, Laelia) can be propagated by using<br />

rhizomes or stolons divided into sections containing about five pseudobulbs.<br />

8. Tubers. In plants such as yam (Dioscorea spp.) <strong>and</strong> white (or Irish) potato<br />

(Solanum tuberosum), the underground stems are highly enlarged as storage organs<br />

(Figure 3–11). Caladium is a popular tuber plant. Whereas Irish potato tubers are<br />

generally small in size, yam tubers vary widely in size <strong>and</strong> shape, according to the<br />

species, some attaining lengths of several feet. Tubers have nodes <strong>and</strong> axillary buds<br />

called eyes. Tubers develop best under reduced photoperiod (short days) <strong>and</strong> lower<br />

night temperatures. However, shoot development is vigorous under long-day<br />

conditions.<br />

9. Tuberous roots. They lack nodes <strong>and</strong> axillary buds, the buds are present only at the<br />

shoot (proximal) end.<br />

3.4 LEAF<br />

There are five types of leaves: foliage leaves, bud scales, floral bracts, sepals, <strong>and</strong> cotyledons.<br />

3.4.1 FUNCTIONS<br />

The major functions of leaves are the following:<br />

1. Food manufacture. The most widely known function of the leaf is<br />

photosynthesis. This function is performed by foliage leaves, which are the most<br />

readily visible type of leaf.<br />

3.4 Leaf 75

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